1. Field of the Invention
This invention relates generally to the field of dishwashers and specifically to a controller for a dishwasher having alternating liquid flow to spray arms.
2. Description of the Related Art
Washing machines, particularly dishwashers, often have two or more spray arms for directing washing liquid at objects to be washed. Typically, a lower spray arm is located near the bottom of a wash tub and an upper spray arm is located in a middle area or near the top of the wash tub. A pump is provided to deliver liquid from a sump in the bottom of the tub to the spray arms. Commonly, the liquid is delivered simultaneously to both spray arms in more or less equal amounts.
U.S. Pat. Nos. 4,741,353 and 5,264,043, both to Milocco and incorporated herein by reference, show and describe an apparatus and method for alternating liquid flow between the spray arms. A specialized ball valve switches flow from one arm to the other when operation of the pump is interrupted for a certain amount of time. The Milocco references show a programmed electronic controller for operating the pump to achieve proper operation of the valve. It would be desirable to use an electromechanical controller for such an apparatus because of the inherent simplicity and reliability.
Electromechanical controllers for dishwashers are well known, as shown, for example, in U.S. Pat. Nos. 2,771,894; 2,825,665; 3,199,525; 3,439,687; 3,440,399; 3,835,880; 4,159,211; 4,559,959 all incorporated herein by reference. Typically these controllers have a cam wheel defining a plurality of coaxial cam disks each adapted to operate one or more switches. The switches are connected to control different machine functions. The cam wheel is driven by a timer motor. In some installations, the controller is provided with an auxiliary cam wheel to control a specific function of the washer. For example, the auxiliary cam can be connected to control a water valve to provide a brief (about 11 seconds) inlet of water to purge the sump of dirty water at the end of a washing operation. Such controllers are simple, reliable, and adequate for most dishwashing functions. Therefore, it is desirable to adapt an electromechanical timer to control the short and precise lobes required for the Milocco ball valve.